1. Field of the Invention
The present invention relates to a level regulation circuit of a common signal, and more particularly, to a level regulation circuit of common signals of a Liquid Crystal Display (LCD).
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a pixel of a conventional Thin Film Transistor (TFT) LCD. Each pixel of the LCD includes a first sub-pixel and a second sub-pixel. The first sub-pixel includes a TFT 16a, a liquid capacitor C1cO, and a storage capacitor CcsO. The second sub-pixel includes a TFT 16b, a liquid capacitor C1cE, and a storage capacitor CcsE. The TFT 16a of the first sub-pixel and the TFT 16b of the second sub-pixel are electrically connected to the same data line 14(m) and the same scan line 12(n). The storage capacitor CcsO of the first sub-pixel is electrically connected to a first common signal line 240. The storage capacitor CcsE of the second sub-pixel is electrically connected to a second common signal line 24E. Thus, the voltage drops across the storage capacitors CcsO and CcsE can be different.
Please refer to FIG. 2. FIG. 2 is a waveform diagram illustrating voltage level of control signals of the pixel shown in FIG. 1. Vs(m) represents the voltage signal of the data line 14(m). Vcom represents the common voltage. Vg(n) represents the voltage signal of the scan line 12(n). VgH represents the high-level voltage of Vg(n), and VgL represents the low-level voltage of Vg(n). VcsO represents the voltage signal of the first common signal line 240. VcsE represents the voltage signal of the second common signal line 24E. VcsH represents the high-level voltage of VcsO and VcsE. VcsL represents the low-level voltage of VcsO and VcsE. V1cO represents the voltage signal of the liquid capacitor C1cO of the first sub-pixel. V1cE represents the voltage signal of the liquid capacitor C1cE of the second sub-pixel. V1c(c) represents the central voltage of the liquid capacitor. The voltage signal VcsO of the first common signal line 240 is complementary to the voltage signal VcsE of the first common signal line 24E. The voltage level of common voltage Vcom is in the middle of the high-level voltage VcsH and the low-level voltage VcsL and serves as the bias voltage of the voltage signals VcsO and VcsE. The voltage signals VcsO and VcsE are square waves.
Since the common voltages Vcom of display panels of LCDs are different, the common voltage Vcom is required to be adjusted for reducing the flicker of the LCD. However, in the above-mentioned LCD, wherein each pixel includes two sub-pixels, the high-level voltage VcsH and the low-level voltage VcsL of the voltage signals VcsO and VcsE can not be adjusted when adjusting the common voltage Vcom. In this way, the flicker of the LCD can not be effectively reduced.